The present invention relates to an electronic apparatus comprising a protection device for data stored in a memory, the device including means for producing a personality data.
The invention likewise relates to a data protection method.
The invention finds interesting applications in the field of portable radio telephones complying with the AMPS standards and others. These apparatus have memories which are capable of containing crucial data, for example: data relating to the serial number which permits of determining the caller and of charging him, or data relating to an prepayment account for radio telephone calls. These data and thus the memory are to be protected to avoid unexpected copies from the side of ill-intentioned persons, or also to certainly avoid the theft of said memory.
From U.S. Pat. No. 4,727,544 is known a system including such a device. This system is intended for electronic gaming devices. According to this patent, read-only memories which contain crucial data are encoded. This encoding makes it possible to detect any violation or copy being made of said memory. This encoding, which determines the personality data, consists of determining a checksum based on the contents of the memory to be protected. This checksum is stored in the protection device and the checksum is computed again when the circuit in which the memory is arranged is switched on. The new checksum is compared with the stored checksum. If a difference is detected, it is estimated that there has been a modification of the memory and the circuit is then blocked.
The device of the patent cited above may in certain applications be considered to be put into operation, which implies processes which quite often invoke the processor of said device too much, which also has tasks to be carried out in the system containing such a device.
The present invention proposes an apparatus of the above-mentioned type which is particularly simple to use, while offering sufficient guarantee against fraudulent copies.
Therefore, such a device comprises:
a random number generator which produces a number linked with the apparatus containing the device, for forming said personality data,
means for storing said random number in said memory when said device is switched on for a first time and
a comparing device for comparing the number produced by said generator with the number stored on said first switch-on, so as to block the apparatus in the event of divergence.
The inventive idea is based on the fact that the copied or hidden memory can no longer function in another apparatus, because the generator produces a number that is practically characteristic of the apparatus containing said device.
A variant of embodiment is to be noted according to which said generator is formed by:
a voltage divider formed by resistors which have tolerance values of a certain magnitude,
an analog/digital converter for converting the voltage of the voltage divider into a digital magnitude,
first processing means for producing said personality data when the means are switched on for a first time based on said digital magnitude,
second processing means for comparing said personality data with that produced by said generator, after said first switch-on.
This variant of embodiment offers the considerable advantage that such a generator is of minimum cost and very well performs the function of random number generator. It is thus nearly certain that the generator produces a different value for each apparatus, which thus very well characterizes the apparatus into which it is inserted. Furthermore, the analog/digital converter which converts this value is often available anyhow in check circuits which form part of many electronic apparatus and thus does not create additional cost.
It should also be noted that the use of a potentiometer divider for generating a personality data of an apparatus is described in U.S. Pat. No. 4,623,976. However, this magnitude is not used for protection purposes of capital data. Furthermore, for generating this personality data, the differences of value provided by commercial resistors are not taken into account.